CHAPTER YI 



respiration, lungs, skin-breathing, circulation, 

 hearts, and lymph-hearts in amphibians 



Respiration 



Since ampliibians have no ribs to expand their 

 lungs, those which Ijreathe air get their breath by 

 literally swallowing it, but they have muscles which 

 expel it. In the water-haunters with gills, the lungs 

 are mere sacs, without cells or pouches. In the cee- 

 cilians the left lung is small and nearly useless. All 

 the kinds which stay under the water long have cer- 

 tain places in the body where well aerated blood -is 

 stored ; and a large blood supply runs to the skin 

 also. The skin aids the amphibians in breathing, 

 even where there are good lungs, as in the frogs. 

 To be thus useful it must be moist, like the gills of a 

 fish, so that frogs and toads especially have water 

 condensed into the body which they can cause to flow 

 out over the skin. 



In the tailed forms, the body has a "lateral line" 



or series of pores along the side of the body, like that 



of fishes, whence a secretion keeps the skin moist and 



slick. Thev have many other mucus o^lands besides. 



^ye can thus see that frogs may breathe better 



41 



